The difference between storing full-width characters and half-width characters in MySQL

Unfortunately, the MYSQL_DATA_TRUNCATED error occurred again during the company's internal testing of IM, and the log record appeared when mysql_stmt_fetch was called. Based on previous experience, it should be caused by the insufficient length of the given result set binding area. I checked it repeatedly many times but did not find the problem. I have corresponding relationships in the code. For example, for char(20), I will define the char buffer[20] array in my code to store it. It looks so right and perfect. I had no choice but to print each line of data, find the line with the error, and discover that the font was different from the others. for example:

123456789 (half-width)
１２３４５６７８９（full width）

This is not controlled by me entering spaces, but by the full-width and half-width input method. For a full-width character, it is twice the length of a half-width character, and my MySQL uses utf-8, so in the database a full-width character is 3 bytes long.

select length(column) from table_name where…;

Use this to print the length and you can tell. At this time, you need to consider the problem of matching the length of the type in the code with the length of the database field, such as full-width characters or Chinese characters. The char(20) in the database represents 20 characters, not 20 bytes. Please note that when retrieving data, do not use 20 as the result set length.